Semiconductor device packages or integrated circuit (IC) chips may, in general, operate by means of being mounted on a substrate, such as a printed circuit substrate which comprises an interconnection pattern for a circuit to be assembled, to electrically connect with other electrical/electronic devices (e.g. resistors, capacitors, ICs). For the purpose of electrically connecting to other such devices over the interconnection pattern on/in the substrate, the semiconductor device packages or the IC chips comprise a number of external electrodes, while the interconnection pattern on the substrate contains a number of contact pads to be connected to the external electrodes of the semiconductor device packages or of the IC chips.
Various methods for electrically connecting semiconductor device packages or IC chips to printed circuit substrates are well known in the art. An electrically-conductive bond (i.e. a solder bump) is used to mechanically and electrically connect to a printed circuit substrate. One such method uses "bump grid array packages (BGAPs)". A BGAP is defined as a packaged IC chip whose bonding pads bear solder bumps which are substantially truncated-sphere-shaped solidified solder. Now, one method for connecting the BGAP to the printed circuit substrate is described in the following. Firstly, a BGAP is placed so that each solder bump of the BGAP is located on its corresponding contact pads of the substrate. The solder, then, is heated to induce reflow and electrical connection between the BGAP and the substrate, and the BGAP is mounted on the substrate as a result.
A major problem associated with these types of packages or with flip chips (defined as unpackaged IC chips whose bonding pads bear solder bumps which are substantially truncated-sphere-shaped solidified solder) is inducing shear strain in the solder bumps. Shear strain is induced since the solder bumps are not flexible and there is the mismatch of thermal coefficient of expansion between the BGAP (or flip chip) and the substrate. For this reason, adequate solder joint height is needed to minimize the effects of such thermally driven fatigue. Here, the solder joint consists of at least one solder bump. In other words, needed are BGAPs( or flip chips) having solder joints higher than single greatest possible solder ball for a given pitch, pad area, etc. One attempt at a solution to this need is disclosed in Matsui et al., JP. Pat. Application No. Sho 60-156621 filed on Jul. 16, 1985. Matsui et al. describes an IC chip with solder joints which consist of solder bumps and a non-conductive film, and describes a process of fabricating such solder joints. As shown in FIG. 1, the IC chip 100 described in Matsui et al. comprises the solder joints, which consist of solder bumps 103a, 103b and the non-conductive film 107, electrically connected to corresponding bonding pads 102 of the IC chip 100. Furthermore, the non-conductive film contains electrodes 108, such as those consisting of outer layers of wettable copper and inner layers of unwettable titanium, located as corresponding to the solder bumps 103a and 103b. Each solder bump 103a, connected to a corresponding bonding pad 102 of the IC chip 100, may be connected through one of the electrodes 108 indirectly to one solder bump 103b to be connected to a contact pad 112 of a substrate 110.
Such composition of the solder joints prevents the solder bumps 103a and 103b, upon being heated, from being caused to mix with each other and to solidify forming solder joints similar to truncated spheres, each of whose volume is approximately two times greater than that of the solder bump 103a. Consequently, in the process of fabricating the IC chip 100, each solder bump 103a keeps almost the same diameter as its diameter before being electrically connected, through one of electrodes 108, to the corresponding solder bump 103b. Thus, the method described in Matsui et al. has an advantage of being able to increase solder joint height without increasing its diameter.
However, the non-conductive film 107 having the electrodes 108 is essentially employed in the method. Also, it is necessary to arrange the electrodes 108 of the film 107, in the same formation of an array of the external electrodes 102 engaged on an active side of the package 101, as shown in FIG. 1. In other words, the formation of the array of the electrodes 108 of the non-conductive film 107 depends on how the external electrodes 102 of the package 101 are arranged. Therefore, it is necessary to employ a non-conductive film to be assembled so as to correspond to a package applied in the process.